1. Field of the Invention
The present invention relates to a vehicle steering control device and method.
2. Description of the Related Art
Some industrial vehicles such as forklifts are equipped with an all-electric steering control device. The all-electric steering control device changes the wheel angle (steering angle) of each steered wheel (by detecting the steering wheel angle which is the rotation angle of a steering wheel and driving a steering actuator according to this steering wheel angle.
A configuration of such a steering control device will be further described based on FIG. 6. FIG. 6 is a diagram illustrating a configuration of a conventional steering control device for an industrial vehicle.
As shown in FIG. 6, a steering actuator 6 has a configuration including: an electric motor 7; a pinion 8 fixed on a rotary shaft of the electric motor 7; a rack 9 meshing with the pinion 8; and rods 10A and 10B respectively connecting two left and right (vehicle-width direction) end portions of the rack 9 with left and right steered wheels 1A and 1B. With this configuration, in the steering actuator 6, the electric motor 7 is actuated to rotate the pinion 8 as indicated by the arrow A, and the rack 9 in mesh with the pinion 8 as well as the rods 10A and 10B are thereby moved either to the left or to the right as indicated by the arrow B or C. As a consequence, the steered wheels 1A and 1B are steered either to the left or to the right as indicated by the arrow D or E.
Meanwhile, a steering wheel angle sensor 3 is attached to a rotary shaft of a steering wheel 2 for steering the steered wheels 1A and 1B. The steering wheel angle sensor 3 detects a steering wheel angle which is the rotation angle of the steering wheel 2, and outputs a detection signal of the steering wheel angle to a steering controller 4. The steering controller 4 converts the steering wheel angle detected by the steering wheel angle sensor 3 to a command wheel angle on the basis of a previously-stored correlation between the steering wheel angle and the wheel angle, and outputs the obtained command wheel angle to a motor driver 5. The motor driver 5 drives the electric motor 7 on the basis of the command wheel angle inputted from the steering controller 4. As a consequence, the wheel angle of each of the steered wheels 1A and 1B is made equal to the command wheel angle.
However, the steering wheel 2 and each of the steered wheels 1A and 1B are not mechanically coupled to each other in this all-electric steering control device, which causes the following problems.
(1) Since the reactive force is not transmitted from the steered wheels 1A and 1B to the steering wheel 2, the steering force (which is a force required for an operator to operate the steering wheel 2) is constant regardless of the running state of the vehicle. This deteriorates the steering feeling.
(2) An operator who is not used to the steering easily brings the vehicle into an unstable running state while driving at a high speed since the operator can operate the steering wheel while driving at a high speed with the same steering force as while stopping the vehicle.
To cope with these problems, as disclosed in Patent Document 1 listed below, a steering control device is proposed which is capable of imparting a steering reactive force to a steering wheel. FIG. 7 is a diagram illustrating a configuration of a conventional steering control device capable of imparting a steering reactive force to a steering wheel. Note that, in FIG. 7, the same parts as in FIG. 6 are given the same reference numerals, and their duplicated description will be omitted.
As shown in FIG. 7, this steering control device is equipped with a steering reactive force controller 11, a brake driver 12, and an electric-control brake 13, in addition to the same configuration as in FIG. 6. The electric-control brake 13 is attached to a rotary shaft of the steering wheel 2, and is capable of imparting a steering reactive force to the steering wheel 2 by exerting an electric brake force on the rotary shaft. The steering reactive force controller 11 receives a detection signal of a steering wheel angle (operation angle) from the steering wheel angle sensor 3, obtains a command steering reactive force on the basis of the received steering wheel angle and the previously-stored correlation between the steering wheel angle and the command steering reactive force (target operation torque), and outputs the obtained command steering reactive force to the brake driver 12. The brake driver 12 drives the electric-control brake 13 on the basis of the command steering reactive force inputted from the steering reactive force controller 11, so as to make the brake force of the electric-control brake 13 equal to the command steering reactive force. In this way, the steering reactive force according to the steering wheel angle is imparted to the steering wheel 2. Note that, Patent Document 1 listed below also provides a description that a vehicle speed sensor may be provided so that the command steering reactive force (target operation torque) may be associated with the steering wheel angle and a vehicle speed.